linux-kernel - Re: [RFC patch 04/15] arm64/entry: Use generic syscall entry function

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Message-ID: <20190920122116.GA21231@arrakis.emea.arm.com>
Date:   Fri, 20 Sep 2019 13:21:17 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Marc Zyngier <maz@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-arch@...r.kernel.org
Subject: Re: [RFC patch 04/15] arm64/entry: Use generic syscall entry function

On Thu, Sep 19, 2019 at 05:03:18PM +0200, Thomas Gleixner wrote:
>  #ifdef CONFIG_ARM64_ERRATUM_1463225
> @@ -97,19 +97,16 @@ static void el0_svc_common(struct pt_reg
>  
>  	regs->orig_x0 = regs->regs[0];
>  	regs->syscallno = scno;
> +	/* Set default error number */
> +	regs->regs[0] = -ENOSYS;

I think this corrupts the first argument of all valid syscalls.
SC_ARM64_REGS_TO_ARGS uses regs[0] instead of orig_x0. ptrace should be
fine since it calls syscall_get_arguments() which uses orig_x0.

We could change the SC_ARM64_REGS_TO_ARGS macro though (in theory there
shouldn't be any performance hit as it's already cached).

>  
>  	cortex_a76_erratum_1463225_svc_handler();
>  	local_daif_restore(DAIF_PROCCTX);
>  	user_exit();
>  
> -	if (has_syscall_work(flags)) {
> -		/* set default errno for user-issued syscall(-1) */
> -		if (scno == NO_SYSCALL)
> -			regs->regs[0] = -ENOSYS;
> -		scno = syscall_trace_enter(regs);
> -		if (scno == NO_SYSCALL)
> -			goto trace_exit;
> -	}
> +	scno = syscall_enter_from_usermode(regs, scno);
> +	if (scno == NO_SYSCALL)
> +		goto trace_exit;
>  
>  	invoke_syscall(regs, scno, sc_nr, syscall_table);

-- 
Catalin